The source of light may be either gas, oil, or candle, it does not matter which, though on the score of convenience perhaps gas has some advantage. Whichever be employed the light should stand on a mark on the table, or bench, and the printing frame be placed at a given distance from it—two feet is a good average distance. Correct exposure can only be learnt by experiment, but working under the fixed conditions which I have prescribed will render it a tolerably easy matter to ascertain. The quickest and easiest way of finding out the proper amount is to give a graduated exposure to the negative in the manner which I will now describe.
One of the packets of bromide paper is opened in the non-actinic light of the dark-room, and a sheet of the paper laid, coated side down, on the negative in the printing frame ; the sensitive side may be known by its tendency to curl inwards ; the back of the frame is then replaced, and the frame itself placed at the two-feet mark from the light. All but one-third of the negative should be covered up by a piece of card larger than the frame, the light turned up, and an exposure of say five seconds given, the card is then moved so that two-thirds of the negative is uncovered, ten additional seconds being counted, when the card is completely withdrawn, a further ten seconds being allowed. We shall thus have given three different exposures to the same print, so that, although this print will be valueless from an artistic point of view, we shall be able upon development to see which exposure was most nearly correct To work bromide paper successfully one must use non actinic light of a suitable character. The paper is very much less sensitive than an ordinary dry plate, therefore light of a very different character may be employed ; ruby light is unsuitable and unnecessary. Good yellow light, and plenty of it, should be used. I find the ordinary yellow fabric sold for about 9d. a yard to be the most suitable material to employ. In fact, the light should be such that the print of an ordinary book may be read with comfort by it.
The most suitable developer for bromide prints is the ferrous oxalate. Hydroquinone is recommended by some workers, but it is not one that I can advise the beginner to employ, as with it there is a great tendency to obtain results of a "soot and whitewash" character. The deve loper, as ordinarily employed, is made by adding one part of the saturated solution of sulphate of iron to six parts of the saturated solution of oxalate of potash (the iron must always be added to the oxalate, or a precipitate would result); but in my own practice I slightly modify this strong developer by adding to it an equal bulk of distilled water, my plan being to give a rather full exposure, and develop with a solution well restrained by dilution with water. I have given a great deal of attention to the development of bromide prints, and I have found that this treatment of the paper generally gives the finest results. The image comes up slowly, and density is not acquired so rapidly as when the concentrated developer is used. The development is conse
quently more under control, and can be more easily arrested when the desired effect is obtained. The gradation of the prints, too, is much better than when the ordinary method is followed Development is carried out in the same manner as with a plate. The exposed paper is soaked for a few minutes in a porcelain dish filled with clean water. The water is poured off, and the developer flowed over the paper in an even wave. If sufficient solution is used this can easily be done. The great thing is to avoid bubbles ; if any form they should be removed with a camel-hair brush. The dish must be rocked so as to cause the developer to flow backwards and forwards over the paper. The development of the image should be gradual, and even if the exposure has been incorrect, with the dilute developer recommended, the image will never rush up, as is sometimes the case when normal solutions are used, unless the exposure has been very excessive. The print should be allowed to develop just a trifle denser than it is required to be when finished, as there is a little reduction of density in fixing. It is impor tant to arrest development at the right moment, and with out hesitation. The solution, therefore, must be poured off into the measure promptly, and about 2 oz. of clearing solution, composed of acetic acid i oz., water GO oz., poured over. This will at once arrest development, and will remove any deposit of iron from the pores of the paper. Its use should never be dispensed with, or impurity or yellowness of the whites may result. The prints may remain in the solution about two minutes, when they must be thoroughly washed, to remove all traces of acid, before being trans ferred to the fixing bath, which should be composed of hyposulphite soda 2 oz., water 10 oz. After two hours of thorough washing they may be removed, and hung up by one corner to dry. The surface being gelatinous, they must not be dried between blotting paper.
In concluding this chapter I will refer to one or two matters of detail which may assist the novice in securing good results.
First, as to exposure : very thin negatives should be printed with a weak light, dense ones with a strong light. Excessive exposure will produce a grey-looking print with out contrast ; under-exposure will, on the contrary, give very great contrast and an absence of detail. Over-exposed prints may possibly be saved by further diluting the deve loper with water, and adding one or two drops of a 10 per cent. solution of bromide of potassium. Development is much faster in hot weather than in cold, and the time occupied in developing will have some effect upon the result, for prints which take a long time to develop will appear hard, while those that develop quickly will be soft. The best colour can only be obtained by giving a correct exposure. Perfect freedom from contamination with other chemicals is of primary importance in bromide work ; the least trace of hypo. or pyro. would be fatal to good results, and indelible stains would be produced.